Come posso scrivere la formula per il nitruro di potassio?

La risposta corretta è #K_3N#.

To see how we arrived at that answer, we first have to examine the electronic configuration of #K# e #N#.

#K# ha #19# electrons and has the following electronic configuration #rarr 1s^2 2s^2 2p^6 3s^2 3p^6 4s^1#

As potassium obeys the octet rule, it will lose one electron in its #4s# subshell to achieve a stable octet noble gas configuration, forming the ion, #K^+#.

Configurazione elettronica di #K^+ rarr 1s^2 2s^2 2p^6 3s^2 3p^6#

#N# has seven electrons and has the following electronic configuration #rarr1s^2 2s^2 2p^3#

Nitrogen also obeys the octet rule and will gain three electrons to achieve stable octet noble gas configuration, forming the negative nitride ion, #N^-3#.

Configurazione elettronica di #N^-3rarr1s^2 2s^2 2p^6#

Each nitrogen atom gains three electrons from three potassium atoms and each potassium atom loses one electron to a nitrogen atom. In this process each potassium atom becomes #K^+# ion and each nitrogen atom #N^-3# ione.

The first 1:30 of questo video shows the movement of the electrons in potassium nitride (wordlessly).